This invention relates to means for securing cutting elements on drag type drill bits, and more particularly to mechanical interlocking means to secure diamond cutting elements firmly within a metal matrix on drag type drill bits.
Any number of various diamond products are used commercially in drill bits. One such diamond product is a synthetic polycrystalline diamond (PCD) cutting element which in general is fabricated from synthetic and/or natural diamond crystals under heat and pressure in the presence of a catalyst to form the polycrystalline structure.
In one application the PCD cutting element is surface set in a metal matrix provided to hold the diamond cutting element in place, the matrix normally being attached to a steel blank on the drill bit by a suitable metallurgical and mechanical bond. While a natural diamond is normally sufficiently thermally stable to withstand such a bonding process, the polycrystalline diamonds (PCD) forming the cutting elements have at times been thermally unstable at the temperatures of around 2000.degree. F. to 2100.degree. F. used in the formation of the metal carbide matrix. At times, thermal degradation in the PCD cutting elements occurs from expansion of the residual catalyst used in the process of forming the PCD.
However, thermal stable PCD cutting elements are commercially available today and generally have thermally stable properties similar to those of natural diamonds so that such cutting elements can be set in a metal carbide matrix in generally the same way as natural diamonds. It is advantageous to have as large a cutting face as can be obtained, as this improves the cutting action of the drill bit. Polycrystalline synthetic diamonds which are commercially available in a variety of geometric shapes and sizes are manufactured and sold by the General Electric Company under the name "Geoset". As an example, the polycrystalline synthetic diamonds sold under the mark "Geoset 2103" are generally triangular, prismatic-shaped elements and have been found to be substantially thermally stable for the bonding process involved in the metal carbide matrix securing the synthetic diamond cutting elements.
As examples of the prior art, reference is made to U.S. Pat. Nos. 4,491,188 dated Jan. 1, 1985; 4,499,958 dated Feb. 19, 1985; and 4,515,226 dated May 7, 1985; which disclose thermally stable diamond cutting elements in the form of a triangular prism secured to the bit in such a manner that a portion of the planar cutting face is exposed for the cutting operation. However, it is noted that a substantial portion of the planar surface of the cutting face in these references is covered by the adjacent carbide matrix in order to obtain the required securement, thereby reducing the cutting efficiency of the PCD cutting elements.